1. Field of the Invention
The present invention relates to a die clamping apparatus of an injection molding machine, a press or the like.
2. Description of the Prior Art
One example of a die clamping apparatus in the prior art is illustrated in FIG. 10.
In this figure, reference numeral 50 designates a support frame 50. On one end of this support frame 50 is fixedly secured a fixed die plate 54 having a fixed die 52 mounted thereon, and on the other end of the support frame 50 is slidably mounted a movable die plate 58 having a movable die 56 mounted thereon in an opposed relationship to the fixed die plate 54. On the fixed die plate 54 are provided a plurality of hydraulic cylinders 60, and tie bars 64 extend from internal pistons 62 of these respective hydraulic cylinders 60 towards the movable die plate 58. In addition, at one portion of the fixed die plate 54 is fixedly secured a boost cylinder 66. A tip end portion of a rod 70 connected to an internal piston 68 of this boost cylinder 66 is appropriately fixed to one portion of the movable die plate 58. Furthermore, at the tip end portions of the tie bars 64 are respectively formed threads 72, and on the side of the movable die plate 58, provided with insert holes 74 through which the tie bars 64 are inserted, opposite to the movable die 56 are disposed half-nuts 76 adapted to mesh with the threads 72 of the tie bar 64. An appropriate moving means 80 is provided for moving the half-nuts in directions nearly at right angles to the axes of the above-mentioned insert holes 74.
The tie bars 64 have such dimensions that their tip ends may be located at positions somewhat separated from the insert holes 74 of the movable die plate 58, and at one portion of each tie bar 64 is provided an adjustable stop ring 78. In this case, in order to allow the insert hole 74 in the movable die plate 58 and the tie bar 64 to be aligned smoothly, the end of the insert hole 74 is tapered. In addition, during a standby condition of the tie bars 64, positioning of stopper rings 78 provided on the tie bars 64 is effected in such a manner that just before the closure of the dies when the movable plate 58 is moved, the stop ring 78 provided on the tie bar 64 engages the fixed die plate at the end of the insert hole 74 in the movable die plate 58 on the side of the die mounting surface, and the threads 72 provided on the tie bar 64 mesh with the half-nut 76 provided on the movable die plate 58. It is to be noted that reference numeral 92 designates a seal member of the hydraulic cylinder 60.
In the die clamping apparatus having the above-described structure, upon the closing of the dies, if the movable die plate 58 is moved towards the fixed die plate 54 by feeding pressurized oil into one oil chamber 84 of the boost cylinder 66, then just before the die closure of the fixed die 52 and the movable die 56 is completed, the stop ring 78 provided on the tie bar 64 is engaged with the end of the insert hole 74 in the movable die plate 58. At this moment, the half-nut 76 provided on the movable die plate 58 is moved in the directions nearly at right angles to the axis of the insert hole 74 by the moving means 80 to mesh with the threads 72 formed on the tie bar 64. As a result, a fixed coupling between the tie bar 64 and the movable plate 58 can be easily achieved. Subsequently, if pressurized oil is fed into one oil chamber 86 of the hydraulic cylinder 60 provided on the fixed die plate 60, the movable die plate 58 is moved towards the fixed die plate 54 by directly moving the tie bar, and thus, die clamping for the fixed die 52 and the movable die 56 can be achieved.
However, the die clamping apparatus in the prior art as described above is subject to various problems as enumerated below:
(1) The stop ring 78 provided on the tie bar 64 engages with the fixed die plate at the end of the insert hole 74 in the movable die plate 58 just before completion of the closure of the dies as described above. Accordingly, the inner piston 62 of the hydraulic cylinder 60 is preliminarily positioned to attain such an engaging relationship. This positioning varies depending upon the thickness of the dies 52 and 58 when they are closed. PA1 To that end, the hydraulic cylinder 60 must have a stroke that is large enough to be adapted to the variable range of thicknesses of the dies used in this die clamping apparatus, and consequently, as the variable range of the thicknesses of the dies to be used becomes large, the cylinder stroke must also be large. PA1 (2) In addition, the tie bar 64 also serves as a rod of the hydraulic cylinder 60, and so, it tends to be correspondingly as thick and long as the die clamping apparatus is large. Since this rod is only supported in a cantilever-like state at the seal member 92 of the hydraulic cylinder 60, the tie bar 64 tends to tilt due to its own weight, and hence it becomes unable to be centered with the insert hole 74 in the movable die plate 58. Furthermore, oil leakage from the location of the seal member 92 tends to increase. In order to make this arrangement practically available, various contrivances for preventing this tie bar from tilting are necessary. PA1 (3) As described previously, the tie bar also serves as a rod of the hydraulic cylinder 60, and the portion of this rod moving in and out of the hydraulic cylinder is disposed at a location close to where an operator comes frequently and where the rod portion is apt to be trod by operator's safety shoes; and moreover, the rod is liable to be damaged by being struck by a die during replacement of dies. If the rod is damaged, then there would be a serious problem in that oil leakage would occur. PA1 (4) The half-nut 76 and the threaded portions 72 of the tie bar 64 must be preset to a positional relationship in which when the stop ring 78 has engaged the die plate at the edge of opening of the insert hole 74, the phases of the respective threads are matched and can mesh. So if the tie bar 64 should rotate within the hydraulic cylinder 60, the above-mentioned phases would become unmatched. PA1 (5) It is necessary to make the stop ring 78 engage the die plate at the edge of opening of the insert hole 74 just before closure of the dies, and when the replacement of dies has been effected, for instance, when a thin die is replaced with a thick die, there is a problem that even the work associated with preliminarily feeding pressurized oil to the head side of the hydraulic cylinder 60 to make the tie bar 34 advance is troublesome and time-consuming. PA1 (1) One end of each of the tie bars is fixedly secured to one of the fixed die plate and the movable die plate. PA1 (2) A ram having an insert hole for the tie bar of a hydraulic cylinder for clamping dies is provided in the other of the fixed die plate and the movable die plate. This ram is not directly coupled to the tie bar. PA1 (3) At the outlet of the insert hole is provided a half-nut or a locking block. PA1 (4) At the tip end portion of the tie bar are formed threads or circumferential grooves to be engaged with the half-nut or locking block over a length corresponding to the range of the thicknesses of the dies to be used. PA1 (5) Between the aforementioned other die plate and the half-nut or locking block is provided stopper means, which can adjust the movement and positioning of the ram with respect to the axis of the tie bar insert hole. A part of the ram is caused to butt against the stopper means to perform the positioning of the ram, and the half-nut or locking block is brought into pressing contact with the ram to allow it to move back and forth for adjustment, thereby setting the half-nut or locking block at a position at which it can mesh with the threads or circumferential grooves on the tie bar. PA1 (1) Due to the fact that the length of the threads on the tie bar is chosen to correspond to the variable range of the thicknesses of the dies to be used, and the half-nut is allowed to move for adjustment, the threads on the tie bar and the half-nut can be surely meshed with each other. PA1 (2) Since the tie bar does not also serve as a rod of a hydraulic cylinder as in the prior art, oil leakage does not occur. PA1 (3) Accordingly, even if the tie bar is damaged, there is no need to repair it as is the case with the prior art apparatus. PA1 (4) Since the tie bar is fixedly secured to one of the fixed die plate and the movable die plate, it never rotates about its axis during operation, and so, upon matching the phases of the threads, the adjustment can be performed according to preset phase values. PA1 (5) Phase matching for the threads or circumferential grooves on the tie bar can be achieved by moving the half-nut or locking block a minute amount in the lengthwise direction, by means of a movement adjusting device, and hence, even in the event that the thicknesses of the dies have changed as a result of the replacement of dies, the phase matching can be achieved in a short period of time. PA1 (6) When the tie bar is mounted to the movable die plate, since the driving means such as the hydraulic cylinder for opening or closing the half-nut or locking block is mounted to the fixed die plate, there is no need to provide a hydraulic hose or similar accessory parts on the movable die plate; hence, the peripheral structure of the movable die plate can be comparitively simple, the movable die plate can be moved with the minimum necessary power, and also problems caused by damage of the hose or the like can be reduced.